Transcript 98-366 Slides Lesson 3

Understanding Wired
and Wireless Networks
Lesson 3
Objectives
Twisted-Pair Cable
• Wired networks are still the most common type
of physical connection that computers make.
• Twisted-pair cable is the cable most commonly
used in local area networks.
• It’s relatively easy to work with, flexible,
efficient, and fast.
• A single twisted-pair cable has eight wires; they
are copper conductors that transmit electric
signals.
Twisted-Pair Cable
• These eight wires are grouped into four
pairs: blue, orange, green, and brown.
• Each pair of wires is twisted along the entire
length of the cable, and all of the pairs are
twisted together as well.
• The reason the wires are twisted is to reduce
crosstalk and interference.
Twisted-Pair Patch Cable
Twisted-Pair Cable with the Wires Exposed
Twisted-Pair Cable with the Wires
Straightened
568B, 568A, and BOGB standards
Types of Patch Cables
• Straight through cable –
– Most common type of patch cable.
– Used to connect a computer to a central
connecting device like a switch.
• Crossover cable
– Used to connect like devices to each other,
for example, a computer to another
computer, or a switch to another switch.
Tools Used with UTP Cables
MDI and MDI-X Ports
• Network adapters normally have an MDI port; this
stands for medium dependent interface.
• However, in order for computers to communicate
with other devices, the wires have to cross
somewhere.
• But instead of using crossover cables to connect
computers to central connecting devices such as
switches, these central connecting devices are
equipped with MDI-X ports (medium dependent
interface crossover), which take care of the cross.
Patch Panel and RJ45 Jack
Tools
• The tools necessary to make the
connections between patch panels and RJ45
jacks include a cutting tool, a wire stripper, a
punch down tool, and a testing device
known as a continuity tester, which tests all
of the pins of a connection one by one.
Tools
Attenuation
• Generally, twisted-pair cables can be run
100 meters before the signal degrades to
such a point that it cannot be interpreted by
the destination host.
• If a cable needs to be run farther, a signal
repeater, a hub, or switch can be used.
– Otherwise, fiber optic cable is the solution
because it can be run much farther than
twisted–pair cable.
Twisted Pair Categories
• Twisted-pair cables are categorized
according to the frequency at which they
transmit signals and their data transfer rate
or speed.
Interference
• Interference can be a real problem with
twisted-pair networks, or any networks for
that matter.
• Interference is anything that disrupts or
modifies a signal that is traveling along a
wire.
Electromagnetic Interference (EMI)
• This is a disturbance that can affect electrical
circuits, devices, and cables due to
electromagnetic conduction and possibly
radiation.
• Just about any type of electrical device causes
EMI: TVs, air conditioning units, motors,
unshielded electrical cables (Romex), and so on.
• Copper-based cables and network devices should
be kept away from these electrical devices and
cables if at all possible.
Shielded Twisted-Pair (STP) Cables
• example shielded twisted-pair (STP) cables.
STP cables have an aluminum shield inside
the plastic jacket that surrounds the pairs of
wires.
Radio Frequency Interference (RFI)
• This is interference that can come from
AM/FM transmissions and cell phone
towers.
• It is often considered part of the EMI family
and is sometimes even referred to as EMI.
• Filters can be installed on the network to
eliminate the signal frequency being
broadcast by a radio tower, although this will
usually not affect standard wired Ethernet
networks.
Data Emanation
• One serious issue with data networks, especially
networks with copper-based cabling is data
emanation (also known as signal emanation).
• This is the electromagnetic (EM) field that is
generated by a network cable or network device,
which can be manipulated to eavesdrop on
conversations or to steal data.
• Data emanation is the most commonly seen
security risk when using coaxial cable, but it can
also be a security risk for other copper-based
cables such as twisted pair.
Data Emanation
• There are various ways to tap into these (EM) fields in
order to get unauthorized access to confidential data.
• To alleviate the situation, you could use shielded
cabling or run the cabling through metal conduits.
• You could also use electromagnetic shielding on
devices that might be emanating an electromagnetic
field.
• This could be done on a small scale by shielding the
single device, or on a larger scale by shielding an entire
room, perhaps a server room.
– This would be an example of a Faraday cage.
Crosstalk
• Another common type of interference is
crosstalk.
• Crosstalk is when the signal that is transmitted
on one copper wire or pair of wires creates an
undesired effect on another wire or pair of wires.
• This first occurred when telephone lines were
placed in close proximity to each other. Due to
the fact that the lines were so close, the signal
could jump from one line to the next
intermittently.
Crosstalk
• When it comes to twisted-pair cabling,
crosstalk is broken down into two categories:
– Near end crosstalk (NEXT) occurs when there
is measured interference between two pairs
in a single cable, measured on the cable end
nearest the transmitter.
– Far end crosstalk (FEXT) occurs when there
is similar interference, measured at the cable
end farthest from the transmitter.
Plenum-Rated
• Cables that are installed inside walls or above drop
ceilings where they cannot be accessed by
sprinkler systems in the case of a fire should be
plenum-rated or low-smoke rated.
• Plenum-rated cables have a Teflon coating that
makes them more impervious to fire.
• They are used in these situations because
standard twisted-pair cables have a PVC jacket,
which can emit deadly gas into the air that
ultimately gets breathed in as hydrochloric acid.
Fiber Optic Cable
• Fiber optic cable transmits light (photons)
instead of electricity, and this light is
transmitted over glass or plastic.
• Glass is known as the media for fiber optics,
just like copper is known the media for
twisted-pair cabling.
• The glass or plastic strands in fiber optic
cabling are extremely small; in fact, they are
measured in microns.
Types of Fiber Optic Cable
• Single-mode
– Fiber optic (SMF) is a cable with an optical
fiber that is meant to carry a single ray of
light—one ray of light, one mode.
– This type of cable is normally used for longer
distance runs, generally 10 km and up to 80
km.
Types of Fiber Optic Cable
• Multi-mode fiber optic (MM)
– Cable with a larger fiber core, capable of
carrying multiple rays of light.
– This type of cable is used for shorter distance
runs, up to 600 meters.
– Though much shorter than single mode fiber
runs, this is still six times the distance of
twisted-pair cable runs.
Fiber Optic Cables
Wireless Networks
• Wireless devices might allow for central
connectivity of client computers and handheld
devices.
• Or, they might offer an extension of connectivity
to a pre-existing wireless network and could be
used to connect entire local area networks to
the Internet.
• In addition, some wireless devices can be
connected directly to each other in a point-topoint fashion.
Wireless Access Point
• By far the most well-known wireless device is
the wireless access point or WAP.
• This device quite often also acts as a router,
firewall, and IP proxy.
Wireless Network Adapters
• Wireless network adapters allow for
connectivity between a desktop computer or
laptop and the wireless access point.
• They come in many shapes and sizes,
including USB, PC Card, ExpressCard, and of
course, as an internal PCI or PCI Express
adapter card for a personal computer.
Wireless Repeater
• A wireless repeater is used to extend the
coverage of a wireless network.
• Due to the fact that most WLANs only have a
range of about 100 feet or so (depending on
the standard), wireless repeaters are often
needed to extend that signal further.
Wireless Bridge
• A wireless bridge is similar to a wireless
repeater, but the bridge can connect
different 802.11 standards together; this is
known as bridge mode.
Wireless LAN (WLAN)
• Wireless LAN or WLAN is a network composed
of at least one WAP and at least one computer
or handheld device that can connect to the
WAP.
• Usually these networks are Ethernet based, but
they can be based off other networking
architectures.
• In order to ensure compatibility, the WAP and
other wireless devices must all use the same
IEEE 802.11 WLAN standard.
WLAN Standards
Wireless Encryption Options
Wireless Modes
• There several different ways to connect to a
wireless network
– Infrastructure mode - It occurs when wireless
clients connect to and are authenticated by a
wireless access point,
– Ad-hoc mode - All of the clients communicate
directly with each other.
Service Set Identifier (SSI)
• When utilizing infrastructure mode, the base
unit (normally a WAP) will be configured with
a service set identifier (SSID).
• This then becomes the name of the wireless
network, and it is broadcast over the
airwaves.
• Thus, when clients want to connect to the
WAP, they can identify it by the SSID.
Wireless Settings
Summary
• To recognize wired networks and media types. This
includes identifying twisted-pair cable, cabling tools,
and testers. You also learned what can interfere with
twisted-pair cabling and how to avoid it, and you read
about a slew of wiring standards you should know for
the real world. You also learned some of the basics
about fiber optic cabling and some of the standards
attached to these extremely quick cables.
• To comprehend wireless networks. This included
wireless devices, wireless settings and
configurations, wireless standards, and encryption
protocols.